Overload protected electric switch



Sept 13, 1966 J. F. SULLiVAN 3,272,941

OVERLOAD PROTECTED ELECTRIC SWITCH Filed Oct. 2, 1964 2 Sheets-Sheet 1INVENTOR.

JAMES F. SULL/I/AIV Sept 13, E966 J. F. SULLIVAN 3,272,941

OVERLOAD PROTECTED ELECTRIC SWITCH Filed. Oct. 2, 1964 2 Sheets-Sheet Zzo/a United States Patent Pennsylvania Filed Oct. 2, 1964, Ser. No.401,081

This invention relates to electric switches, and more particularly toswitches provided with means for opening the circuit in case ofexcessive flow of electric current therethrough.

As is well known, it is common practice to place a a thermally operatedcircuit breaker in an electric circuit in order to open the circuit incase it is subjected to an overload. Circuit breakers have to be resetafter they have opened, and of course they occupy space that may be at apremium in a given instrument or appliance. It has therefore beenproposed to incorporate the circuit breaker in the switch housing and toreset the breaker by means of the control shaft of the switch. It hasbeen found, however, that resetting such a circuit breaker has adverselyaffected the sensitivity and accuracy of response of the bimetal thermalelement of the breaker, that excessive arcing may occur when the circuitbreaker opens, and that the circuit breaker may not reclosesatisfactorily.

It is among the objects of this invention to provide an electric switchcontaining a circuit breaker, in which the circuit breaker occupies verylittle space, in which the circuit breaker is automatically reset whenthe switch is opened by its control shaft, in which arcing is minimizedon opening, in which arcing cannot occur when the breaker is reset, inwhich the sensitivity of the breaker is not impaired by frequentresetting, and in which the circuit breaker can always be reset orclosed satisfactorily.

In accordance with this invention, electric contacts are mounted insidea switch housing, where they can be opened and closed by a controlshaft. A bimetallic conductor strip is secured at one end in fixedposition to one of the contacts. Besides the other end of the stripthere is a circuit breaker contact. The strip has a laterally projectingcontact end normally latched onto this breaker contact, from which thestrip is adapted to bend and spring away when overheated by excessiveelectric current flowing therethrough. Extending lengthwise of theconductor strip along the side thereof opposite its contact end is aresilient reset strip, one end of which is anchored in the housingadjacent the fixed end of the other strip. The reset strip is spacedfrom the conductor strip while the latters contact end is latched ontothe breaker contact. The control shaft actuates means for bending thereset strip to force its free end toward the adjacent end of theconductor strip when the shaft is operated to open the switch.Therefore, if the conductor strip has become unlatched from the breakercontact, the free end of the reset strip will push the contact end ofthe conductor strip back into latching engagement with the breakercontact. If desired, one of the switch conas the circuit breakercontact, in which case the stationary end of the conductor strip issecured to the contact previously referred to as the breaker contact.

The preferred embodiment of the invention is illustrated in theaccompanying drawings, in which FIG. 1 is a rear view of my switch;

FIG. 2 is a horizontal central section through the switch and part of avolume control secured to the front of the switch;

FIG. 3 is a side view of the switch, with its side wall broken away toshow the interior;

FIG. 4 is a vertical section taken on the line IVIV of FIG. 2;

FIG. 5 is an enlarged fragmentary vertical section taken on the line VVof FIG. 2, showing only the circuit breaker;

FIG. 6 is a fragmentary section taken on the line VI-VI of FIG. 5; and

FIG. 7 is a fragmentary view similar to FIG. 2, but showing the switchclosed.

Referring to the first six figures of the drawings, in which the switchis shown open, the switch that is illustrated is similar to thepush-pull switch shown in Dressel Patent 2,947,832. As in that patent, acontrol shaft 1 is rotatably and slidably mounted in a bushing 2 securedto the front of the suitable volume control unit 3 when the switch is tobe combined with a volume control. The bushing is threaded and adaptedto extend through a hole in a panel and receive a nut for rigidlymounting the bushing in place. The shaft has a non-circular centralportion 4 that is splined in a head 5 of insulating material rotatablymounted in the volume control housing. The head carries the usualcontact (not shown) that slidably engages a resistance element 6 in thefront of the control housing. The rear end of the shaft extends backthrough a central opening 7 in the back of the volume control and onthrough a similar opening in the metal front wall 8 of a switch housingthat has a cylindrical side wall 9 integral with its front wall. Thefront of the switch housing is welded or otherwise rigidly attached tothe back of the volume control housing.

The control shaft extends back into the switch housing and, in its rearposition, is spaced a short distance from the rearwall 10 of thehousing. This wall is made of insulating material, such as moldedplastic, and supports a pair of fixed electric lug-like contacts 11 and12 that are disposed quite close together between the center of the walland one side of the housing. The contacts extend through the back wallof the housing and project behind it to form electric terminals 13 and14.

In order to engage and electrically connect the fixed contacts, abridging contact 15 can be used. This bridging contact is carried by oneend of an arm 16 that is formed from a plate of insulating material. Thearm is inclined to the shaft and is provided with an opening 17, throughwhich the shaft extends. The opening is considerably larger than theshaft so that the arm will not engage it. As shown in FIG. 4, theopening preferably is formed from two slots intersecting each other toform a T, with the cross bar of the T parallel to the bridging contactand close to it. The stem of the T extends from the opposite side of itscross bar toward the end of the arm remote from the contacts. Shoulders1 8 (FIG. 4) are thus provided by the sides of the cross bar thatconnect with the stem of the opening. These shoulders are set insemicircular notches 19 (FIG. 2) in the edges of a pair of tongues 20cut from the front wall of the switch housing and bent backwardly intoparallel relation on opposite sides of the control shaft. The positionsof the tongues in the ends of the cross bar of opening 17 prevent arm 16from To hold arm shoulders 18 in the tongue notches, a coil spring 21 isdisposed in the stem of opening 17 and has one end hooked around theadjacent end of the arm and the opposite end hooked onto the groovedrear end por tion of the shaft behind the arm. In this position thespring also holds the adjoining end of the arm in its rear position andits free end in its forward position, as shown in FIG. 2, with thebridging contact spaced from the fixed contacts.

It will be seen that with this construction, pulling the control shaftforward to the position shown in FIG. 7 will-likewise pull the inner endof the spring forward to a location in front of notches 19 and therebycause the opposite end of the spring to snap the adjoining end of thearm forward and swing the bridging contact back against fixed contacts11 and 12 to close the switch as shown in FIG. 7. During this movementof the arm, it swings on an axis passing through its shoulders in thetongue notches, the tongues 20 thereby serving as bearing members foroscillation of the arm. When the bridging contact strikes the fixedcontacts it will align itself with them because it is formed from a barthat has forwardly bent ends extending loosely through oversizedopenings 22 (FIG. 4) in the arm and then bent toward each other. Whenthe shaft is pushed in again, the coil spring will snap ion to swing thebridging contact away from the fixed contacts to open the switch. Coilspring 21 does not create side thrust on the shaft that might cause itto bind, because the side thrust is balanced or nearly counteracted bymeans of a compression spring 23 that is located in front of the coilspring and compressed between the side wall of the switch housing andthe side of the control shaft. By pushing laterally against the shaft inone direction, this spring prevents the coil spring from pulling theshaft off center in the opposite direction.

The compression spring also provides a very good electrical connectionbetween the control shaft and the switch housing and thereby insuresgood grounding of the shaft. Another advantage of compression spring 23is that it can serve to limit forward movement of the control shaft inthe switch. This is done by providing the rear end portion of the shaftwith an integral enlargement 24 that will strike the compression springwhen the control shaft has been pulled forward a predetermined distance.

'It is a feature of this invention that a thermally operated circuitbreaker is combined with this switch in series with it. Accordingly, athird fixed contact 26 is mounted in the switch housing on the back wallat the end of switch arm 16 opposite to the bridging contact. This thirdcontact is at the same side of the control shaft as one of the otherfixed contacts, such as contact 12, and preferably is in a place more orless parallel to it. One of the contacts 12 or 26, preferably contact26, serves as a circuit breaker contact. The edge of the circuit breakercontact away from contact '12 is rolled outwardly to form a curvedsurface as shown in FIG. 5. Suitably fastened to the other contact, inthis case contact 13 by means of a rivet'27, is one end of a bimetallicelectrical conductor strip 28. This strip is positioned on edge relativeto the back wall of the housing and extends across the shaft and theside of the breaker contact facing the shaft. The free end of the striphas a laterally projecting contact end 29 that resembles a hook and thatnormally is latched onto the curved edge of the breaker contact. Thecontact end of the strip is bent at an angle to the rest of the stripand may be provided with a reversely curved end portion. Also, it isdesirable to secure a facing 30 of good contact material to the innersurface of this bent portion of the strip for engagement with thebreaker contact. The breaker contact extends through the back wall ofthe housing and becomes a projecting electric terminal 31. Terminals 13and 31 are connected into an electric circuit so that current will flowthrough the switch as long as it is closed and the conthe arm in theopposite directongue 35 out of ductor strip is latched onto breakercontact 26. The strip is so constructed that if it is overheated byexcessive electric current flowing through it, its bent contact end 29will tend to straighten and release itself from the breaker contact,whereupon the strip will spring away from that contact and swing towardthe shaft to break the circuit like a blown fuse. Even when the stripcools and returns from its far dotted line position in FIG. 5 to itsintermediate dotted line position, it will not engage the breakercontact, but will remain spaced from it.

In order to reset the circuit breaker, a resilient reset strip 32 isprovided, which extends lengthwise of the conductor strip in the spacebetween it and the shaft, as shown in FIG. 5. One end of the reset stripis anchored in the switch housing adjacent the riveted end of theconductor strip. One convenient way of doing this is to provide thefront of the back wall With an integral projection 33 provided with alaterally opening recess 34, and punch a the reset strip for projectioninto this recess. The tongue is held in the recess by a boss 36projecting from the back wall and engaging the reset strip on the sideopposite its tongue. The free end of the reset strip may be doubled uponitself adjacent the contact end of the conductor strip to add to itsresiliency but, as shown by dotted lines in FIG. 5, they do not touch aslong as the switch is closed and the conductor strip is latched onto thebreaker contact.

After the conductor strip has sprung away from circuit breaker contact26, due to overheating, the control shaft of the switch is pushed in toseparate the bridging contact from the adjoining fixed contacts. Thismovement of the shaft pushes an actuator 38, attached to its inner end,against the adjoining side of the reset strip and thereby bends thatstrip away from the axis of the shaft as shown in full lines in FIG. 5to force its free end toward the breaker contact. If both the controlshaft and the reset strip are made of metal, actuator 38 should be aninsulating material. Preferably, the front edge of the reset strip isprovided centrally with an inclined lug 39 that is engaged by aninclined surface on the actuator to bend the strip outwardly. Theactuator presumably has a conical end for engaging the inclined lug. Asthe free end of the reset strip is swung outwardly, it engages the freeend of the conductor strip and bends that strip outwardly until thecontact end snaps over the breaker contact as shown in full lines inFIG. 5.

As long as the conductor strip is engaging the breaker contact, thereset strip performs no work when it is swung back and forth by themovements of the control shaft. When the switch is overheated and theconductor switch swings away from the breaker contact, it will lightlystrike the free end of the reset strip, which will dampen the vibrationsthat would otherwise occur and possibly cause arcing between the breakercontact and the conductor strip.

It will be seen that the open circuit breaker cannot be reclosed untilthe switch has been opened, because the inward movement of the shaftperforms the two operations in sequence, with the bridging contactmoving away from the fixed contacts first. Therefore, the circuitbreaker is never reset on a live circuit, but when the switch is closedagain the circuit is ready to operate.

The reset strip, by transmitting a force from the central control shaftto the free end of the conductor strip, does not distort or stretch thebimetallic element, so the sensitivity and accuracy of response of thatelement is not impaired by frequent resetting. The resetting force isapplied to the end, not the center, of the thermal element. Also, thereset strip, by its resiliency, is able to compensate for anyaccumulation of tolerances in the switch, 7 thereby assuringreengagement of the circuit breaker strip with the circuit breakercontact.

According to the provisions. of the patent statutes, I have explainedthe principle of my invention and have illustrated and described what Inow consider to represent its best embodiment. However, I desire to haveit understood that, within the scope of the appended claims, theinvention may be practiced otherwise than as specifically illustratedand described.

I claim:

1. An overload protected electric switch comprising a housing, a pair offixed electric contacts inside the housing, one of said contacts being acircuit breaker contact, a thermally responsive bimetallic conductorstrip secured at one end to the other contact, the strip having alaterally projecting contact end normally hooked onto said breakercontact, said strip being adapted to bend and spring away from thebreaker contact when overheated by excessive electric current flowingtherethrough, a third fixed contact beside one of said pair of fixedcontacts, a movable bridging contact in the housing, a control shaft formoving the movable contact into and out of engagement with said thirdcontact and the fixed contact beside it, a resilient reset stripextending lengthwise of the conductor strip along the side thereofremote from said circuit breaker contact, means in the housing anchoringone end of the reset strip adjacent said other fixed contact, the resetstrip being spaced from the other strip while said contact end is hookedonto the breaker contact, and means actuated by the control shaft forbending the reset strip to force its free end toward the adjacent end ofthe conductor strip when the shaft is operated to open the switch,whereby if the conductor strip has become unhooked from the breakercontact the free end of the reset strip will push said contact end backinto hooked-on engagement with the breaker contact.

2. An overload protected electric switch comprising a housing, a pair offixed electric contacts inside the housing, one of said contacts being acircuit breaker contact, a thermally responsive bimetallic conductorstrip secured at one end to the other contact, the strip having alaterally projecting contact end normally hooked onto said breakercontact, said strip being adapted to bend and spring away from thebreaker contact when overheated by excessive electric current flowingtherethrough, a movable contact in the housing, a control shaft formoving the movable contact into and out of engagement with one of thefixed contacts, a resilient reset strip extending lengthwise of theconductor strip along the side thereof remote from said circuit breakercontact, means in the housing anchoring one end of the reset stripadjacent said other fixed contact, the reset strip being spaced from theother strip while said contact end is hooked onto the breaker contact,and means mounted on the rear end of the control shaft and engageablewith the central portion of the reset strip for bending the reset stripto force its free end toward the adjacent end of the conductor stripwhen the shaft is operated to open the switch, whereby if the conductorstrip has become unhooked from the breaker contact the free end of thereset strip will push said contact end back into hooked-on engagementwith the breaker contact.

3. An overload protected electric switch comprising a housing, a pair offixed electric contacts inside the housing, one of said contacts being acircuit breaker contact, a thermally responsive bimetallic conductorstrip secured at one end to the other contact, the strip having alaterally projecting contact end normally hooked onto said breakercontact, said strip being adapted to bend and spring away from thebreaker contact when overheated by excessive electric current flowingtherethrough, a movable contact in the housing, an axially movablecontrol shaft for moving the movable contact into and out of engagementwith one of the fixed contacts, a resilient reset strip extendinglengthwise of the conductor strip along the side thereof emote from saidcircuit breaker contact, means in the housing anchoring one end of thereset strip adjacent said other fixed contact, the reset strip beingspaced from the other strip while said contact end is hooked onto thebreaker contact, said strips being disposed beside the shaft andextending across it, and means actuated by the control shaft for bendingthe reset strip to force its free end toward the adjacent end of theconductor strip when the shaft is operated to open the switch, wherebyif the conductor strip has become unhooked from the breaker contact thefree end of the reset strip will push said contact end back intohooked-on engagement with the breaker contact.

4. An overload protected electric switch comprising a housing havingfront and back Walls connected by a side wall, a bushing rigidly mountedin front of the front wall, two fixed electric contacts in the housingmounted on its back wall, a bimetallic conductor strip secured at oneend to one of said fixed contacts in a position edgewise to the backwall and extending across one side of the other fixed contact, the striphaving a laterally projecting contact end normally latched onto saidother contact, said strip being adapted to bend and spring away fromsaid other fixed contact when overheated by excessive electric currentflowing therethrough, a resilient reset strip extending lengthwise ofthe conductor strip along the side thereof opposite said contact end,means in the housing anchoring one end of the reset strip adjacent saidone fixed contact, the reset strip being spaced from the other stripwhile said contact end is latched onto the other fixed contact, a thirdfixed contact mounted beside one of said two fixed contacts, a switcharm movably mounted inside the housing, an electric bridging contactcarried by said arm, a control shaft mounted in said bushing andoperatively connected with said arm to move said bridging contact intoand out of engagement with said third fixed contact and the fixedcontact beside it, and means actuated by the control shaft for bendingthe reset strip to force its free end toward the conductor strip whenthe shaft is operated to open the switch, whereby if the conductor striphas become unlatched from the adjoining fixed contact the free end ofthe reset strip will push said contact end back into latching engagementwith that adjoining contact.

5. An overload protected push-pull electric switch comprising a housinghaving front and back walls connected by a side wall, the front wallhaving a central opening through it, a bushing rigidly mounted in frontof the front wall in line with said opening, a control shaft slidablymounted in the bushing and extending back into the housing, a switch arminside the housing inclined to the shaft and provided with an openingloosely receiving the shaft extending therethrough, means rockablymounting the arm on an axis extending across the shaft, meansoperatively connecting the shaft and arm for rocking the arm on saidaxis as the shaft is pulled and pushed, an electric bridging contactcarried by the back of the end of the arm normally nearest said frontwall, a pair of fixed electric contacts in the housing mounted on itsback wall at one end of the arm in position to be engaged by thebridging contact when it is swung back toward them by pulling the shaft,a third fixed contact in the housing mounted on its back wall behind theopposite end of the arm, one of said fixed contacts being a circuitbreaker contact, a bimetallic conductor strip secured at one end to afixed cont-act at the end of said arm opposite to the end adjacent saidbreaker contact, said strip being positioned edgewise to the back walland extending across the axis of said shaft and the shaft side of thebreaker contact, the strip having a laterally projecting contact endnormally latched onto the breaker contact, said strip being adapted tobend and spring away from the breaker contact when overheated byexcessive electric current flowing therethrough, a resilient reset stripextending lengthwise of the conductor strip between it and said shaft,means in the housing anchoring one end of the reset strip adjacent thesecured end of the conductor strip, the reset strip being spaced fromthe other strip while said contact end is latched onto the breakercontact, and means actuated by the shaft for bending the reset strip toforce its free end toward said breaker contact when the shaft is pushedto open the switch, whereby if the conductor strip has become unlatchedfrom the breaker contact the free end of the reset strip will push saidcontact end back into latching engagement with the breaker contact.

6. An overload protected electric switch according to claim 5, in whichsaid last-mentioned means has a forwardly and inwardly inclined surface,and said reset strip is provided with a central inclined lug at itsfront edge 8 for engagement by said inclined surface to move that striptoward the conductor strip.

References Cited by the Examiner UNITED STATES PATENTS 2,191,588 2/1940Sattler. 2,947,832 8/1960 Dressel 20067 2,958,748 11/ 1960 Barden et al.

10 BERNARD A. GILHEANY, Primary Examiner.

H. B. GILSON, Assistant Examiner.

Disclaimer 3,272,941.-James F. Sullivan, St. Marys, Pa. OVERLOADPROTECTED ELECTRIC S'WITCH. Patent dated Sept. 13, 1966. Disclaimerfiled J an. 13, 1969, by the assignee, Stack-pole Carbon Company. Herebyenters this disclaimer to claims 1 2 and 3 of said patent.

[Ofiicial Gazette April 29, 1969.]

1. AN OVERLOAD PROTECTED ELECTRIC SWITCH COMPRISING A HOUSING, A PAIR OFFIXED ELECTRIC CONTACTS INSIDE THE HOUSING, ONE OF SAID CONTACTS BEING ACIRCUIT BREAKER CONTACT, A THERMALLY RESPONSIVE BIMETALLIC CONDUCTORSTRIP SECURED AT ONE END TO THE OTHER CONTACT, THE STRIP HAVING ALATERALLY PROJECTING CONTACT END NORMALLY HOOKED ONTO SAID BREAKERCONTACT, SAID STRIP BEING ADAPTED TO BEND AND SPRING AWAY FROM THEBREAKER CONTACT WHEN OVERHEATED BY EXCESSIVE ELECTRIC CURRENT FLOWINGTHERETHROUGH, A THIRD FIXED CONTACT BESIDE ONE OF SAID PAIR OF FIXEDCONTACTS, A MOVABLE BRIDGING CONTACT IN THE HOUSING, A CONTROL SHAFT FORMOVING THE MOVABLE CONTACT INTO AND OUT OF ENGAGEMENT WITH SAID THIRDCONTACT AND THE FIXED CONTACT BESIDE IT, A RESILIENT RESET STRIPEXTENDING LENGTHWISE OF THE CONDUCTOR STRIP ALONG THE SIDE THEREOFREMOTE FROM SAID CIRCUIT BREAKER CONTACT, MEANS IN THE HOUSING ANCHORINGONE END OF THE RESET STRIP ADJACENT SAID OTHER FIXED CONTACT, THE RESETSTRIP BEING SPACED FROM THE OTHER STRIP WHILE SAID CONTACT END IS HOOKEDONTO THE BREAKER CONTACT, AND MEANS ACTUATED BY THE CONTROL SHAFT FORBENDING THE RESET STRIP TO FORCE ITS FREE END TOWARD THE ADJACENT END OFTHE CONDUCTOR STRIP WHEN THE SHAFT IS OPERATED TO OPEN THE SWITCH,WHEREBY IF THE CONDUCTOR STRIP HAS BECOME UNHOOKED FROM THE BREAKERCONTACT THE FREE END OF THE RESET STRIP WILL PUSH CONTACT WND BACK INTOHOOKED-ON ENGAGEMENT WITH THE BREAKER CONTACT.